Is it possible to constraint an object on a vertice?
I'm going on memory here but basically you do the parent procedure, select the child, and with shift held select the parent.  Press Tab and you'll be in edit mode for the parent model.  Select a vertice and choose that option in the pop-up.  Press Tab again to return to object mode.  If the vertice is at the model's origin point, when the object rotates, the child shouldn't because the vertice won't be moving in any axis.  It's an ideal way to attach a camera to models.